Question

Wow, I cant believe how many problems related to loading and saving to internal memory.
I find that I can only Save to a protected area related to my app.
I am not sure I can even create a directory in that area.
Storing to the SD I’ve mastered, but the requirements are that if no sdcard is available or has been removed the app continues be able to load and save user settings. I have 120 different data items so shared preferences are not the way. Cache is not persistent.

I currently have as a method :

public static void SaveUserPrefs()
{
 try
{
 //FileOutputStream fos = openFileOutput("userPrefs.dat", Context.MODE_PRIVATE);
 FileOutputStream fos = new FileOutputStream( "userPrefs.dat"); 
 BufferedOutputStream bos = new BufferedOutputStream(fos); //to get a buffered stream  
 ObjectOutputStream oos = new ObjectOutputStream(bos);
 oos.writeFloat(versionNumber);
 oos.writeInt(autoWifiStart);
 oos.writeInt(autoAirPlane);
 ... many more items and file close

I get file not found exceptiom /userPrefs.dat Read only file system
You would think the same code would work either external or internal, but doesnt.
I have tried the comment out code also with same results.
Where and how do I save this data?
And do I need to do something different to load it?
I do have permission set to save_external_Storage.

Answer 1

I find that I can only Save to a protected area related to my app.

On internal storage, this is correct.

I am not sure I can even create a directory in that area.

Use getFilesDir() to retrieve a File object pointing to your application’s area on internal storage, then call mkdirs() on the File object to create subdirectories. The latter is standard Java file I/O.

I have 120 different data items so shared preferences are not the way.

There is no particular limit on the number of items in SharedPreferences. SharedPreferences are stored in an XML file.

I get file not found exceptiom /userPrefs.dat Read only file system

You have supplied an invalid path. Use getFilesDir() to get the File object pointing to your application’s area on internal storage, then use the appropriate File constructor to create a File object pointing to your specific file on internal storage. Use that latter File object in your FileOutputStream constructor. Again, other than getFilesDir(), this is standard Java file I/O.

You would think the same code would work either external or internal, but doesnt

That code does not work with external storage, either, as the path you have supplied is not on external storage.

Where and how do I save this data?

Personally, I would never use ObjectOutputStream. For 120 items, I would definitely consider a SQLite database, otherwise I would serialize my data to JSON or XML. Any of those options are easier to debug than ObjectOutputStream, IMHO.

And do I need to do something different to load it?

You will need to construct the appropriate File object pointing to the file in question for use with some type of InputStream, following standard Java file I/O.

I do have permission set to save_external_Storage.

WRITE_EXTERNAL_STORAGE is not necessary for writing to internal storage.